Field of the Invention
The present invention relates to a pre-mold for a microphone assembly, to microphone assemblies and methods of manufacturing the same.
Description of the Related Art
In the art a plurality of semiconductor devices and housings of the same are known. A specific field of housings is the field of housings or packages for Si-microphone chips or micro-electro-mechanical system (MEMS) microphone chips. These MEMS microphone chips comprising thin (e.g. in the order of magnitude of a few 100 nm) oscillating membranes on the active side of the MEMS microphone chip. Additionally, the membrane may be metallized so that the oscillation can be sensed by way of a capacitive coupling with an electrode arranged opposing the membrane. An important factor of the performance of housed Si-microphone is the rear volume which denotes the volume behind the membrane, when seen in the direction of the arriving sound wave, since this rear volume represents a compensation volume for the oscillating membrane. This rear volume has to be provided in the package.
The rear volume for the membrane of a MEMS microphone is provided by etching the MEMS microphone chip from the backside to expose the membrane. Then the MEMS microphone chip is mounted on and wire bonded to a substrate comprising several layers and typically produced by printed circuit board techniques. After the mounting and wire bonding of the MEMS microphone chip (and of an optional ASIC chip) a lid or housing is glued to the substrate for covering the microphone. In order to let pass the sound waves to the membrane of the MEMS microphone chip the lid comprises a through-hole. The lid may be formed by electric conductive material and may be electrically connected to the ground terminal of the substrate so that the lid as well provides a shielding against electromagnetic interference.
FIG. 7 schematically shows such a MEMS microphone assembly 700, comprising a multilayer substrate 701 onto which an ASIC 702 is placed and covered by a passivation or protection layer 703. Furthermore, a MEMS microphone chip 704 is mounted to the multilayer substrate 701 and comprising a rear volume 705 used as a balancing or compensation volume for an oscillating membrane 706 of the microphone. The MEMS microphone chip 704 and the ASIC 702 are electrically connected by wires 707 to the substrate. For covering the MEMS microphone chip and the ASIC a lid 708 is provided which comprises a through-hole 709 and is connected to the multilayer substrate 701.
However, there is still potential room to improve the manufacturing process of such microphone assemblies.